Experimental evaluation of ripening behavior: Down-Flow vs. Up-Flow rapid sand filters

Abstract

Filter ripening is progressive development of media charge and build-up of collector efficiency, during starting phase of granular filtration. In the present work, a comparative study of ripening behavior was carried out by conducting simultaneous laboratory filtration experiments on Down-Flow (DF) and Up-Flow (UF) sand filters. The artificial influent was used for filtration studies. It was prepared to replicate pretreated low turbidity surface water. The Filter Ripening Sequence (FRS) curve for the UF filter was observed to be significantly distinct. It was corroborated that the ripening depends on filtration rate (v) for the both filters. Enhancement in the ripening performance of the both filters was witnessed for the influents with less negative zeta potential of influent particles (ζp). Further, the technique of Extended Terminal Sub-fluidized Wash (ETSW) with cationic polymer in wash water was also tested to improve ripening process. It was found effective in reducing initial degradation of effluent for the both filters. However, the ETSW with polymer modified wash water resulted in considerable increase in head loss during ripening for the DF filter. Particularly, the incremental increase in head loss subsequent to polymer modified ETSW was less for the UF filter.